1. Field of the Invention
The present invention is in the field of cryogenics and specifically relates to a valve for controlling the flow of cryogenic fluids. The valve uses unconventional materials in a design that results in the valve having very low heat leak, excellent strength, vacuum and pressure integrity, and modest manufacturing cost.
2. The Prior Art
In a low heat leak cryogenic valve, the manual operating handle or power operator is at room temperature. Either of these is connected to the valve sealing element or plug by a stem which is housed within a stationary sleeve called the bonnet extension. The bonnet extension is generally substantially larger in diameter than the stem in order to allow insertion and removal of the valve plug. The valve stem, bonnet extension, and annular space between them act as paths for the influx of heat. Likewise, the space within a tubular valve stem will allow heat to enter, both by radiation and by conduction.
The most common approach to reducing the influx of heat is to use conventional materials that have low thermal conductivity and to minimize the cross sectional area of the conductive path consistent with maintaining the strength of the parts.
When this traditional approach was applied by the present inventor to a 1.5 inch cryogenic valve, the heat leak was reduced from approximately 5 watts to approximately 2 watts.
Thereafter, the present inventor was faced with the need to reduce the heat leak to approximately 0.5 watt--a factor of 10 relative to the original conventional 1.5 inch valve. To solve this formidable problem, a fresh approach was needed, and the solution is the subject of this application.